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Brain Tumors: Diagnosis

How are brain tumors diagnosed?

If your healthcare provider thinks you might have a brain tumor, you will need some exams and tests to be sure. Diagnosing a brain tumor starts with your healthcare provider asking you questions. He or she will ask you about your health history, your symptoms, risk factors, and family history of disease.

Your healthcare provider will also give you a physical exam. He or she will likely examine you for possible signs of brain or spinal cord problems. The exam will test things like your reflexes, muscle strength, sensation, eye and mouth movement, vision, coordination, and alertness.

Types of imaging tests

Magnetic resonance imaging (MRI). An MRI scanner uses magnets and strong radio waves to make pictures of the brain. MRIs are very useful in diagnosing brain tumors because they allow your doctor to "see through" your skull. This results in clearer pictures of the brain. A technician might inject a special dye into your vein. This makes it easier to see the difference between a tumor and normal brain tissue. An MRI can show slices of the brain from many different angles. It can show smaller details better than other scans. An MRI is especially helpful in finding tumors in the back part of the brain called the posterior fossa. It is also better at finding tumors in the spinal cord.

Computed tomography (CT) scan. A CT scan is a type of X-ray that creates detailed pictures of the brain. Many images of the brain are taken as the X-ray scanner moves around your head. A computer combines these many images into a useful picture. Sometimes a technician injects a special dye into a vein before the CT scan to enhance the difference between normal and abnormal tissue. This test is not used as often as MRI to look for brain tumors, but it can be helpful in some situations. A special form of CT scan, known as CT angiography (CTA), may be used to look at the blood vessels around a tumor to help plan surgery.

Positron emission tomography (PET) scan. For a PET scan, a technician injects a small amount of a radioactive substance into your vein. It’s usually glucose, a type of sugar. Fast-growing tissue, such as a tumor, absorbs this substance and can be seen by a special type of scanner. The radioactive material used in this test is not dangerous. It will leave your body in about 6 hours. A PET scan can help your doctor tell the difference between an active, growing tumor and damage from radiation therapy or a scar from surgery. Tumors light up while damaged tissue doesn’t.

Magnetic resonance spectroscopy (MRS). An MRS scan can determine the metabolites inside the tumor. Sometimes, this test is used to determine if a growth is an active tumor or a mass of radiation damage (necrosis).

Angiogram. An angiogram is a series of X-rays taken after a technician injects a special dye into one of your blood vessels. It may also be called arteriogram or venogram, depending on which type of blood vessel is used. A technician also inserts a catheter into one of your large blood vessels, usually in your groin, and then positions it with the help of an X-ray. After injection, the dye flows through the blood vessels in your brain and can be seen on X-rays. These X-rays show the tumor and the blood vessels that lead to it, which helps doctors plan surgery. This test is used less often than in the past. CT angiography and magnetic resonance (MR) angiography are now used more often to look at blood vessels in the brain.

Magnetic resonance angiography (MRA) and magnetic resonance venography (MRV). These are special types of MRI tests that can show blood vessels in and around the brain. They are less invasive than an angiogram.

Diffusion tensor imaging (DTI). This is a type of MRI exam that lets the doctor see the neural pathways in your brain. This is useful for surgeons to help plan tumor removal.

Functional magnetic resonance imaging (fMRI). This is an MRI test that can help map which parts of the brain handle important functions such as movement or speech. This can be helpful before surgery.

Skull X-ray. Certain types of tumors can leave calcium deposits. A skull X-ray is very good at seeing these. Skull X-rays will also show changes to the structure of the skull caused by tumors.

Other tests

Lumbar puncture (spinal tap). For this test, a thin, hollow needle is placed into the lower back, into the spinal canal. This is the area around the spinal cord. The fluid pressure in the spinal canal and brain can then be measured. A small amount of cerebrospinal fluid (CSF) can be removed and sent for testing to see if it contains cancer cells. CSF is the fluid that bathes the brain and spinal cord. Other tests may be done on this fluid as well.

Electroencephalogram (EEG). An electroencephalogram (EEG) is a non-invasive test that measures the electrical activity in the brain, called brain waves. Small round discs with wires (electrodes) are placed on your scalp. An EEG can be used to check for seizures.

Your healthcare provider may also determine you will need formal testing of your vision and hearing.

Brain tumor biopsy. If any of these tests suggest that a tumor might be present, a neurosurgeon will probably take a biopsy of the tumor. In most cases, this is the only way to know for sure if a tumor is benign or malignant (and to determine what type of tumor it is), although sometimes doctors can get enough information to make a diagnosis from the imaging tests alone. For a brain tumor biopsy, a doctor takes out as much of the tumor as possible through a bone "window" made in your skull. A pathologist examines this sample under a microscope to see if it is cancer. Another type of biopsy is the stereotactic biopsy. For this biopsy, the neurosurgeon removes a small piece of the tumor with a hollow needle. The needle is carefully guided and placed in the tumor with the help of an imaging test, such as an MRI or CT scan.

Getting your test results

When your healthcare provider has the results of your tests, he or she will contact you. Your provider will talk with you about other tests you may need if a brain tumor is found. Make sure you understand the results and what follow-up you need.

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